Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Worked on a Lennox two speed heat pump HP21. customer complained that it would run for an hour or two and then quit cooling. Gave a general once over, running at 70psi low side, under 200 high side, outdoor was 82 degrees F.

After it ran for 60 min, the low side would gfadually drop to 0 psi and even into the HG zone a little. It never freezes up the indoor coil, not much freon flowing, low side not cold to reversing valve.

From the txv equalizer bypass the line would freeze up down to the low side line and give the compressor some cooling, but not much, a little bit of cold r22 seemed to be flowing through the txv. I did the magnet trick on the receiver check valve that is in the outdoor unit right below the txv, turned it all off and ran the test on the TSC, a code 42 came up, which is a hot windings or ruined compressor sensors. Checked the sensor ohms, and running dc voltage on the TSC terminals for the Compressor sensor, all was well and I suspect it may have been an earlier recall code due to the low side pressure dropping, the volume drops too, as the low side line coming back to the reversing valve is not cold and returning any refrigerant. The high side never changes, not a bit, always holding below 200.

Started it all back up, same problem, only sometimes it is a gradual decline in low side pressure, always to 0, sometimes it happens faster than usual, but back to 0. Tested reversing valve, temperatures are equal from return to compressor, very hot coming from compressor to reversing valve, as one would expect energized in cooling mode.

I'm racking me brains on this one, do I have a back check valve in the outdoor unit or txv? When put in the heat mode, it all runs fine. I have several Lennox and heat pump books, but can't find the solution.

I would check the expansion valve indoor...it would seem your liquid line is restricted somewhere, causing the system to pumpdown...loss of suction pressure...there is probably a restriction entering the expansion valve causing your problem...alot of those lennox indoor expansion valves had flare fittings or compression fittings on the liquid line feeding them...Pump it down, and check for a piece of solder or slag or anything either restricting a screen or the valve itself..good-luck.

Re: lennox hp21 heat pump

Originally posted by mkelley2 Thanks for the input, out of 11 techs no one wants to go near this one. Mike

Most people start blubbering when they hear "Lennox 2 speed", then if you say "Lennox 2 speed heat pump", they run screaming.

I always enjoyed working on them. The HS/HP21 took all the fun out of it though, with the electronic module that saves diagnostic codes.
The old HP11 units were a lot more interesting with all the tangled mass of controls and wiring, especially when I was like the 7th person from the 4th company to work on it in the last month.

love those hp21 units the old hp14 with all the relays and time delays were interesting to
any way did you check the sensing bolb on the tax may be it is working properly or the tube is cracked and the valve isnt working.

lennox hp21 heat pump

Thanks everybody. I guess I know what I get to do this week regarding the indoor txv. I was a little thrown by refrigerant being able to flow through the equalizer on the outside txv, turn the whole txv cold, but not raise the head up some.